Nancy Lanza loved guns, and often took her sons to one of the shooting ranges in the suburbs northeast of New York City, where there is an active community of gun enthusiasts, her friends said. At a local bar, she often talked about her gun collection.

It was one of those guns that was apparently used to take her life on Friday. Her killer was one of her sons, Adam Lanza, 20, who then drove to Sandy Hook Elementary School, where he killed 26 more people, 20 of them small children, the authorities said. He then shot himself.

Nancy Lanza's fascination with guns has become an important focus of attention as investigators sought to determine what caused Adam Lanza to carry out one of the worst massacres in the US's history.

Investigators have linked Nancy Lanza to five weapons: two handguns, a semi-automatic rifle and two traditional hunting rifles. Her son took the two handguns and the semi-automatic rifle to the school.

Law-enforcement officials said they believed the guns were acquired lawfully and were registered.

Nancy Lanza was also reportedly a "survivalist" whose fear of an impending global financial collapse led to her becoming self-reliant, the UK Daily Mail reported.

Nancy Lanza's sister-in-law, Marsha Lanza, 57, said: "She was stockpiling food. We talked about prepping a lot. She was getting ready for the economic collapse.

"I think she had the guns for self-defence because she lived alone", adding that Nancy was "meticulous" and would "never leave the guns out".

The Lanza family had been disrupted by divorce in 2008. Nancy Lanza split from her husband of 17 years, an executive at General Electric, court records show, and he moved out. Adam stayed with his mother.

In a statement on Saturday night, the father, Peter Lanza, said he was co-operating with investigators. "We are in a state of disbelief and trying to find whatever answers we can," he said. "We too are asking why."

He added: "Like so many of you, we are saddened but struggling to make sense of what has transpired."

Nancy Lanza lived in a large colonial home with her son, and had struggled to help him cope with a developmental disorder that often left him reserved and withdrawn, relatives, friends and former classmates said.

At some point, he had dropped out of the Newtown school system. She had an older son, Ryan, who did not live with them.

Marsha Lanza said that Adam Lanza had been home-schooled for a time because his mother was not "satisfied with the school".

His former classmates described Lanza as nervous.

"He was always different — keeping to himself, fidgeting and very quiet," said a classmate, Alex Israel.

"But I could always tell he was a super-smart kid, maybe just socially awkward, something just off about him. The same went for when I went to his house. His mother was always nice to me, she was a kind, typical suburban mum as far as I remember. As time went on, he continued to keep to himself and I branched out more, so not much contact with him after middle school.

"By the time high school came around he did sort of disappear," she added. "I'd see him in the halls walking quickly with his briefcase he carried, but I never had a class with him and never saw him with friends. I was yearbook editor and I remember he declined to be photographed or give us a senior quote or baby picture."

News reports on Friday suggested that Nancy Lanza had worked at the elementary school, but at a news conference the school superintendent said there was no evidence that she had ever worked at the school as a full-time or substitute teacher, or in any other capacity.

The authorities said it was not clear why Adam Lanza went to the school.

Whatever problems Nancy Lanza's son had, she herself was sociable and active in the community, friends said. Lanza, 52, was a slender woman with blonde shoulder-length hair who enjoyed craft beers, jazz and landscaping. She was generous to strangers, but also high-strung, they said, as if she were holding herself together.

She often went to a local restaurant and music spot, My Place, where at beer tastings on Tuesday evenings, she often talked about her gun collection, recalled an acquaintance, Dan Holmes, owner of a landscaping company in Newtown.

"She had several different guns," Holmes said. "I don't know how many. She would go target shooting with her kids."

In a statement on Saturday, other members of the Lanza family called Nancy Lanza a "kind, considerate loving young lady", but did not answer questions about her guns or about her son.

"On behalf of Nancy's mother and siblings," the statement said, "we reach out to the community of Newtown and express our heartfelt sorrow for the incomprehensible and profound loss of innocence that has affected so many."

Many of those who knew Nancy Lanza were at a loss to describe what she did for a living. Louise Tambascio, the owner of My Place, said she had not been working full-time but volunteered occasionally in the community. "She stayed with Adam," Ms Tambascio said, adding that, as a younger child, he "couldn't get along with the kids in school."

Nancy Lanza spoke often of her landscaping, Mr Holmes recalled, and later hired him to do work on her home. Last week, he dispatched a team to put up Christmas decorations at her house - garlands on the front columns and white lights atop the shrubbery.

After the work was complete, she sent Mr Holmes a text: "That went REALLY well! Two people took care of the gardens and gutters and one decorated. Very efficient and everything looks great! Thank you!"

Jim Leff, a musician, often sat next to her at the bar and made small talk, he said in an interview on Saturday.

On one occasion, Mr Leff said, he had gone to Newtown to discuss lending money to a friend. As the two men negotiated the loan, Nancy Lanza overheard and offered to write the man a cheque.

He declined to elaborate, but in a post on his personal website, he said he felt a distance from her that was explained when he heard, after the shootings, "how difficult her troubled son [Adam] was making things for her".

She was "handling a very difficult situation with uncommon grace", he wrote.

She was "a big, big gun fan", he added on his website.

There are many gun enthusiasts in this area, residents said.

When some people who live near the elementary school heard the shots fired by Adam Lanza on Friday, they said they were not surprised.

Neighbours recalled Nancy Lanza as sociable, a regular at Labour Day picnics and "ladies' nights out" for a dice game called bunco.

"We would rotate houses," said Rhonda Cullens, 52, a neighbour since Nancy Lanza moved to Newtown with her husband and two children. "I don't remember Nancy ever having it at her house."

Ms Cullens said Nancy Lanza had not discussed an interest in guns with her, but spoke often about gardening - exchanging the sorts of questions typical of the neighbourhood: What can you plant that the deer would not eat? Is such maintenance worth the trouble for a house like the Lanzas, perched on the back of a steep hill and scarcely visible from the street? "She was complaining, 'Here, I'm doing all this landscaping up here and nobody can see it'," Ms Cullens recalled.

But for many of those on Yogananda Street, where the Lanzas lived and where the police had cordoned off much of the block, the recollections were incomplete.

"Who were they?" said Len Strocchia, 46, standing beside his daughter as camera crews came through the neighbourhood. "I'm sure we rang their door bell on Halloween."

He looked down the block, then turned back to his daughter. "I'm sure of it," he said.

Marsha Lanza, also struggled to make sense of events. "I just don't have an answer," she said, starting to cry. "I wish I had an answer for you. I wish somebody had saw it coming."